Refactor Git provider validations out of dependency factory

We currently have Git provider validations in the `WithGit` function, but we should only be validating on the build itself and not the validations. We should move this over to a separate place where we perform these validations before cluster operations, but after we build the dependencies, potentially in the validations package.

https://github.com/aws/eks-anywhere/blob/main/pkg/dependencies/factory.go#L756-L767

Start by reading pkg/dependencies/factory.go around lines 756-767 and tracing the validations package and dependency build flow. Run the relevant package tests to understand the current behavior. Done means Git provider checks no longer run in WithGit, but run before cluster operations after dependencies are built.

Written by the indexing model from the issue text.